This invention relates to an open hot-water heater which has a hot-water faucet and a water tank provided with a hot-water overflow as well as a device for changing the volume of the water tank. The device for changing the volume of the water tank comprises a lifting valve having a cold-water inlet and a cold-water outlet as well as a lifting device actuated by the lifting valve. When the hot-water faucet is opened, hot water is displaced from the water tank through the hot-water overflow by the inflow of cold water. Upon closing of the hot-water overflow, a water-free space is obtained in the water tank as the valve-lifting device returns into its position of rest.
Thus, it is a characteristic feature of open hot-water heaters, which may also be termed as overflow heaters, that upon dispensing of hot water, cold water flows into the water tank at its lowest zone and the cold water, upon its inflow, delivers to the faucet corresponding hot water quantities from the hot-water overflow which is situated in the highest zone of the water tank. Upon completion of dispensing of water, the water tank is nearly fully filled with water. The water level is situated approximately at the highest location of the hot-water overflow pipe. Upon heating the subsequently introduced cold water, the latter expands and the expanded water leaves the faucet in the form of droplets. The appearance of such dripping water during each heating step is considered as a disadvantageous phenomenon by the consumer and may even prompt a consumer unfamiliar with the causes of the drop formations, to attempt to interfere with the armature of the faucet in an unskilled manner in an endeavor to stop the dripping.
U.S. Pat. No. 4,862,834 discloses an open hot-water heater which is provided with a device for preventing water drip caused by heat expansion. In the hot-water heater disclosed therein the lifting device effecting a change of the volume of the water tank is actuated by a piston valve whose housing is, as a separate component, inserted into the base plate of the water tank. The cold-water inlet for the hot-water tank is divided into two inlet pipe portions by means of the interposed piston valve housing. The two inlet pipe portions are situated externally of the water tank. Connecting the cold-water inlet or cold-water outlet to the piston valve housing as well as joining the water supply to the water tank necessitate complex sealing measures and require a correspondingly time-consuming installation. This leads to an increase in finishing costs, which may render unattractive the price of a mass-produced article of this type.